Gas discharge switching device



Sept. 7, 1954 Filed Nov. 20, 1952 w. M. WEBSTER, .1R

@As DISCHARGE swITcHING DEvIcE 2 Sheets-Sheet l I .\'I 'E NTOR.

MMA

,177012A .we Y

Sept 7, 1954 w. M. WEBSTER, JR

@As DISCHARGE swITcHING DEVICE 2 Sheets-Sheet 2 Filed Nov. 20, 1952 Patented Sept. 7, 1.954

UNITED STATES ATENT OFFICE William M. Webster, Jr., Princeton, N. J., assigner to Radio Corporation of America, a corporation of Deiaware Application November 20, 1952, Serial No. 321,554

.10 Claims. 1

invention relates to gas discharge devices andlparticularly to gas discharge devices that may be operated as a switching device at veryf high frequencies.

'It has long been the object'ofV continuous're- Search and experiments toprovide a gas discharge device; or tube, that can function as a bidirectional,v lowI impedance-switch which will be the'analo'gyof a high speed relay to bei used for computer' applications.

Prior-tothis time, some mechanical devices havebeen used as switches; -or relays, ybut they have had thedisadvantages of operating at comparativelyr low speeds. -Certain types oi vacuum tubes have been used-as switches to overcomesthe low speed limitation but the vacuum tubes have the disadvantage'of highimpedance and thus a high voltage hasbeen necessary to operate the devices.

It is an object of thisinvention to provide a new-and improved: high speed switching device of the gas discharge variety.

It isla' further objectof this invention` to provide a new and novel low impedance switching device Aof the, gas discharge type.

It is a still furtherl object of thisv invention to provide a new and improved' bi-directional, high speed.- low impedance, switching device of the gas discharge type.

These and `other objects have been accomplished in accordance with the general aspects of this inventionfloy` providing agas discharge device' having a 'oi-directional current path. The main current path comprisesat least two thermionic cathodes sothat the mai-n current may Iio'vvv in a'- b'i-di-re'ctional `manner `between the two cathodes. Adjacent thel spa'ce intermediate the two cathcdes, is an auxiliary groupof electrodes that provides an auxiliary discharge and forms a'highly yconductive plasma which extends between the' twol thermionic cathodes when it is desired tohave the cathodes con-duct.

The novel features which are believed to be characteristic v'of l this invention are set forth with particularity in the appended claims. The invention itselfwill best -be understood by referring tof the following description taken in connection lwith the following drawings and in which:

`Figure l isa sectional view through line I-I of Figure 2 -f a" gas discharge device constructed in accordance with this invention;

r'Figure 2 is asectonal view through line'2-2 of Figure l JFigures" *A` and y Ltare schematic diagrams showing methods of operating a gas dischargel device constructed in accordance with this invention;

Figures 5 through 9 are transverse sectional views of gas discharge devices illustrative of Various embodiments of gas discharge ldevices constructed in accordancel with this invention.

Referring now to Figures 1 and 2 in detail,v a gas discharge device IG comprises a gas tight envelope I I having the usual stem I 2 through which the lead-in conductors are sealed in a conventional manner, The electrode assembly is supported by means of the conductors within the envelope as indicated. Between the upper and lower insulating members I3 and I4 are Amounted two main cathodes It and E8. Both cathode I6 and I8 are the usual oxide coated type of thermionic cathode having a non-inductive type of heater I? and I9 respectively extending therein, the leads of which are each connected to support conductors 2@ and 2l in the usual manner. The cathodes I5 and It! are electrically energized by means of conductors 23 and 24 respectively. The upper ends of the main cathode I6 and I8 are crimped in the well known manner to lock the same in place-between insulating members I3 and I4.

Included within the envelope is an auxiliary group oi electrodes comprising an auxiliary thermionic cathodezl, surrounded by an apertured constricting electrode 28, and an auxiliary anode 35. The auxiliary electrodes are supported between insulating members I3 and I4 in a conventional manner and are spaced on opposite sides of the main current path formed by cathodes I6 and I3 so that the auxiliary discharge is substantially perpendicular to the main current path. The auxiliary anode 3E) is energized by means of lead-in 3l in the usual manner. The auxiliary cathode 26 and apertured electrode 28 are also energized by means of conventional leadins (not shown).

The auxiliary cathode 26 is also an oxide coated thermionic cathode and is supported between insulating members I3 and I4. The apertured constricting electrode 28 surrounds the auxiliary cathode 25 with a constricting aperture' 29 arranged so that the auxiliary discharge is directly across the main current path. Auxiliary anode 3@ comprises a metallic plate of conventional design and is spaced on the opposite side of the main current path from auxiliary cathode 25.

Gas discharge device It is processed in the well known manner and, as well known in the art, is provided with a gaseousv atmospherefprior to sealing off. Any suitable gas or mixture of gases may be utilized depending upon the electrode geometry and spacings for the separate embodiments. Furthermore, it is not believed that the gas pressure is critical except that it is preferable to utilize a pressure which will favor the formation of a self-sustaining ionizing discharge. In the tube now being described as being illustrative of this invention, helium may be used at a pressure of approximately 750 microns though other gases and other pressures may also be used.

During operation of the discharge device IG, a difference of potential greater than the ionization potential of the gaseous filling is applied to the auxiliary group of electrodes so that a discharge occurs between auxiliary cathode 26 and auxiliary anode 30. This discharge forms a plasma within the envelope that extends across the main current path. Since the plasma is an extremely low impedance conductor, the impedance across the main current path, i. e. the impedance between main cathodes I6 and I3 is extremely low. The potential difference applied between the main cathodes I6 and I8 is normally well below the ionization potential of the gaseous filling so that no electron discharge occurs between main cathodes I5 and IS unless there is a plasma formed by the auxiliary discharge. In fact when there is no plasma present between the main cathodes IG and I8, there is an open circuit between main cathodes I6 and I8.

After the auxiliary electrodes have discharged, and formed the plasma, the plasma remains for a short instant of time before deionization completely occurs. Because of the deionization time of the device, the main cathodes may conduct either during the auxiliary discharge or during the time immediately after the auxiliary discharge has been cut 01T and before the plasmas have depleted by recombination, diffusion, etc. When the auxiliaiy electrodes are discharging, or during the deionization time, currents 0f the order of an ampere may pass between main cathodes I6 and I8 at a relatively low applied voltage.

When gas discharge device Ill is used as a switching type of device the operation thereof is very similar to an extremely high speed mechanical relay. The maximum frequency at which this device is capable of operating may be in excess of 10,000 cycles per second. The device is constructed in such a manner that current may ow in either direction between two main cathodes I6 and I8 depending upon which is positive with respect to the other. The positive cathode IG or I8 acts as an anode for current in one direction while the other cathode acts as an anode for current in the opposite direction.

The auxiliary discharge is perpendicular to the main load current path so that coupling between the auxiliary discharge and the main load current is substantially reduced. Another method of still further reducing coupling between the `auxiliary discharge and the main load current is to pulse the auxiliary discharge. Thus when the switch is to conduct a given computation, the auxiliary discharge is pulsed and the plasma is formed. During the brief instance when the plasma is still present after the auxiliary discharge is pulsed the computation is made. Before the next computation is to be made, the residual plasma disappears. This action is extremely fast and devices of this type have been operated in this manner at 10,000 cycles per second.

The discharge device IIJ may be controlled by several methods. One method is simple on-off control by varying the potentials on main cathodes I6 and I8. A second method is by modulating the density of the plasma formed by the auxiliary discharge. A signal may be placed on the apertured constricting electrode 28 by means of lead-in 3i and this signal will modulate the density of the plasma in the main current region. Because of the fact that ionization occurs outside the constricting electrode 28, the electrode 28 can completely cut off the electron flow 0f an auxiliary discharge and thus completely modulate the plasma density.

In Figure 3 there is shown a method of operating a gas discharge device constructed in accordance with this invention. The device as shown is the embodiment of a gas discharge as shown in Figures 1 and 2 however, it should be understood that the circuit is applicable to the other embodiments of the invention. In the schematic diagram shown in Figure 3, the auxiliary cathode 26 is connected to the apertured focusing electrode 28 and both are grounded. Main cathode I6 is connected to a proceeding stage I5 of a computer while main cathode I8 is connected to a subsequent switching stage 22 and a firing pulse is applied to anode 30. A ring pulse, i. e. a positive pulse greater than the ionization potential is applied to anode 30 to cause an auxiliary discharge to occur and thus break down the device. The pulse forms a plasma in the device that remains through the deionization time. During the time when the plasma is present, a given computation may be passed by making one of the main cathodes I6 or I8 positive with respect to the other. Preferably, to avoid coupling, the computation is made during the interval of time after the auxiliary discharge occurs and before the plasma is depleted. The proper timing between the auxiliary discharge and the main current computation may be adjusted by means of any conventional timing circuit (not shown).

In Figure 4 there is shown a similar circuit to still further minimize coupling between the auxiliary discharge and the main current path. Here again the embodiment of this invention that is shown in the schematic diagram is the embodiment described in connections with Figures l and Z but the circuit diagram is equally applicable to the other embodiments. In this method of operating gas discharge device ID, the secondary of transformer 'I4 is connected between auxiliary cathode 2B and anode 30. Here again the auxiliary cathode is connected to the apertured focusingelectrode 28. The main cathodes I6 and I8 are connected to proceeding and subsequent stages as shown in Figure 3. When it is desired to render the discharge device conductive for a given computation, a pulse greater than the ionization potential of the medium is applied to the primary of transformer 'I4 and the computation is made as has been described.

This embodiment of the circuit diagram further reduces the coupling between the main current path and the auxiliary discharge path because the auxiliary discharge electrodes are electrically floating except during the time when the auxiliary discharge occurs. In other words, if the pulsed operation of the auxiliary discharge is utilized as has been described, the auxiliary electrodes are electrically floating during the interval of time when the main current computation-is beingmade Due tothe factithat .the auxiliary electrodes-are electrically -iloatingwthey will assumethe. potential of-` the. plasma andthus have. no eiect. upon the. main-current electrodes.

.Referringnow toFigure .5 thereis shownan embodiment of `this invention wherein onezof the main-groups of electrodes includes an anode. 34 and a thermionic cathode 36 electrically -connected -by conductor` within theenvelope. The other main. group .of electrodes- .includes a thermionic cathode 38- and anode 40 .alsoi'electrically connected. by conductor V`3E). `It. should. be noted that opposite thermionic cathode 36 is vlocated anode 40-while `opposite .thermionic cathode 38 is located anode A34. :Since each cathode is.-electrically connected:` to ananodefwhen the device is conducting in agiven direction boththe cathodeV and the anodev of!y the electron receiving end are eiectively-ananode and thusV larger currents may be transmitted through thedevice at the same high frequency. and low impedance as was described in connection withFigures l1 land 2. The auxiliary electrodes-include the sameelements aswas shovvnl and described in connection with Figures 1 and 2 and further description is not deemed necessary at this time. `Main cathodes 36 and.38 aswell, as'main yanodes34 and 40 are supported `within theenvelopeand energized in a conventionalmanner. .The :connections 35- and 3S `may be .any type of electrical conductor such as a rod, or `wire between the respective electrodes.

An alternative structure that. may be usedin thisl embodiment of the invention is -to utilize a composite anode-cathode for each endV oftheI I main current. path. In other Words,.one portion of an anode may be sprayedwith .ernissive material and may also have some typeof heating means if desired.

Referring noWto Figure 6 therewis. shownanother embodiment of .this invention which .permits even larger currents tobe passed-through the main current path. Inthis embodiment one main group of-electrodes. includes athermionic cathode 44 arranged intermediate a pair ofgspaced apart. anodest45 and V46, vvvhile'the.'other-f. main group ofelectrodes includes., a` thermionic cathode arranged-intermediate mainz anodes` 51| and 52. All of the electrodesin a single group are joined by an electrical conductor-4T orz49, respectively. This embodiment vhas the advantage of being capable of. passing extremely. large. current in. a bi-directional manner.

Referring now. to Figure' there .is shownsan embodimentof this invention that .permits additional control between `a pair Aoi .main thermioniccathodes 54 and 56. `in this embodiment, an apertured electrodetI is arranged intermediate the lmain cathodes 54 and `56. to .modulate the main load current when the proper potentials are applied to the apertured electrode 58. The theory that permits a control electrode to modulate electron How in a gas discharge device is explained in av coaopending .applicationof` Edward O. Johnson, Serial No.. Y185,7l5,..iiledSeptember 20, 1950 and assigned to the same assignee as the present invention.

It should be understood thatv any of the ina-in groups of electrodes that Vhave been described in connection with Figures l, 2, 5, and 6, may be utilized with a control electrode intermediate the main groups. It should be noted that one end of the control electrodes 5B is adjacent aperture 59 in the apertured electrode 68 to divide the plasma so that it is Ion both sides of the control; electrode 58 .and thus. allow! impedance conductive. pathy -is connected between vmaincathode 54-and156 AWhen it is .desired forther-tubeto conduct.

.Referring now to Figure 8 there is shownan embodiment. -of thisv invention utilizing'an aperturedanode! (i2l in the auxiliary discharge electrode group. In thisfembodiment an `.auxiliary cathode v63 isv surrounded byy an apertured constrictingaelectrode 64 havingia constricted'raperturefil therein. The aperture-liti.v is arranged to constrict the electron stream and direct ritv toward apertured anode 62. The apertured anode-62 is arrangedl substantially-parallel to the main currentpath between thermionic cathodes 66-and 61. TheI apertures inapertured anode t2l are greater than thefmeanfreeV path ofthe plasma particles toalloW diffusion of the plasma particles through the .apertured .anode 62.

In. operationl of; the l embodiment shown in Figure 8 is a potential greater than the ionization potential of themedium isfapplied between.I auxiliary cathode 63-and aperturedanode'62 .to vform theyplasrnav by. means of kthe auxiliary. discharge. When theauxiliary discharge occurs -a` plasma is j'formed in thev spaced outside apertured` electrode 64. fT-his;.plasmaplls the main= current path. partly by-diifusion throughapertured electrodefBZ and partly by` ions produced inthe main current region bythose high energy electrons which;.penetrateV aperturedI electrode 62. -Ifdesired,; pulsedtype operation .may be 'utilizedfas has previously been described. .The operation of the 1main-currentpath as Wellas other-embodiments. of the ymain current velectrodes has previously been described and further description is not .deemed` necessary at this time.

. Anzadvantage -of usinguan aperturedv anode=62 is that in `.theyabsence oa ring pulse theaperturedf anode 62 willrelectrostatically shieldthe balance ofthetube from the auxiliary cathode 63.

.Referring novv.to Figure-9; there -isY shown. a further embodiment-of thisainvention utilizing composite aperturedgrid-anode `68. In. this embodiment,.an auxiliary cathodell is surrounded byfan apertured; constricting electrode v212; as has been described. The main currentpath isgbetweenthermionic.-cathodcs Beand 1G. 4Arranged intermediate the `cathodes 69.. and-10 .is a' portion.of.the composite-grid-anode 68. -The remainder of thecomposite grid-anodef is.ar ranged substantially parallel to the "main-current path. Thegqpontion -of' composite grid-anoda 5' that isparallel tothe main currentl Vpath-.should have apertures .that yare `larger than the mean free-.;r ath-.ofl the plasma particles togpermit the plasma to diffuse-through to the main-current path.

in operation of thegas discharge 'device shown in. Figure 9, f a poten-tial: dierence greater than the ionization potential of= the. medium is=ap plied' between-auxiliary'. cathode l tand the compositef grid-anode G8. Thisapotential diierence causes a discharge to occure'between these'relectrodee.` resultingnin .a plasma. .The plasma. diffuses :inta` theumainzcurrent pathwand will. permit conduction.betweencathodesS19-and i6. The potential.-diierence` appliedpbetween .cathodes' 69 and Villa should be less than.- thefionizationxpotential of the medium and the potential applied to both cathodes v6i] and 'Ill should be near the potential of the composite grid-anode 68. The reason for this is that a signal applied to the com.- posite grid-anode 68 should modulate the main current flow between cathodes 69 and 10 but it should be greater than the ionization potential of the medium with respect to auxiliary cathode Il to establish the auxiliary discharge.

While there have been described and illustrated specific embodiments of the invention, it will be obvious that various changes and modifications may be made therein without departing from the spirit thereof. It is, therefore, intended to cover all such modifications which come within the scope of the appended claims.

I claim:

1. A gas discharge device, comprising a` sealed envelope having an ionizable medium therein, a pair of spaced apart thermionic cathodes dening a main load current path Within said envelope, and a group of auxiliary electrodes including an auxiliary thermionic cathode surrounded by an apertured constricting electrode for producing an auxiliary discharge within said envelope.

2. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a pair of spaced apart thermionic cathodes defining a main load current path within said envelope, and a group of auxiliary electrodes including an auxiliary thermionic cathode surrounded by an apertured constricting electrode for producing an auxiliary discharge Within said envelope, the aperture in said apertured electrode be`- ing arranged so that said auxiliary discharge is substantially perpendicular through said main load current path.

3. A gas discharge device as in claim 2 further comprising a control electrode intermediate said pair of cathodes.

4. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a pair of spaced apart thermionic cathodes denning a main load current path within said envelope, and a group of auxiliary electrodes comprising an anode and an auxiliary thermionic cathode surrounded by an apertured constricting electrode, said auxiliary electrodes being arranged on opposite sides of said main load current path whereby said auxilary discharge is substantially perpendicular through said main current path.

5. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a pair of spaced apart main groups of electrodes Within said envelope each group including at least one main anode and a thermionic cathode electrically connected together, each of said main groups of electrodes being one end of a loi-directional main load current path through said device, and an auxiliary group of electrodes comprising an auxiliary thermionic cathode and apertured focusing electrode and an anode, said auxiliary cathode being partially surrounded by said apertured focusing electrode, and said auxiliary electrodes being arranged on opposite sides of said main current path whereby an auxiliary discharge is substantially perpendicular through said main current path.

6. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a pair of spaced apart main groups of electrodes within said envelope each group including a main anode and a main thermionic cathode electrically connected together, each of said main `groups of electrodes being one end of a bi-directional main current path through said device, and an auxiliary group of electrodes comprising an auxiliary thermionic cathode, an apertured constricting electrode and an anode, said auxiliary cathode being partially surrounded by said apertured constricting electrode, and said auxiliary electrodes being arranged on opposite sides of said main current path whereby an auxiliary discharge is substantially perpendicular through said main current path.

7. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a pair of spaced apart main thermionic cathodes comprising a main current path within said envelope, a group of auxiliary electrodes arranged on one side of said main current path including an auxiliary thermionic cathode a constricting electrode and an apertured electrode, said constricting electrode partially surrounding said auxiliary cathode to direct an auxiliary discharge substantially perpendicular to said main current path, and said apertured electrode arranged substantially parallel to said main current path.

8. A gas discharge device as in claim 7 wherein the apertures in `said apertured electrode are larger than the mean free path of the positive ions of said ionizable medium.

9. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a pair of spaced apart main thermionic cathodes within said envelope comprising a main current path, a group of auxiliary electrodes arranged on one side of said main current path including an auxiliary thermionic cathode a constricting electrode and an apertured electrode, said constricting electrode partially surrounding said auxiliary cathode to direct an auxiliary discharge substantially perpendicular to said main current path, and one portion of said apertured electrode being arranged substantially parallel to said main current path while the other portion of said apertured electrode extends intermediate said main cathodes.

10. A gas discharge device, comprising a sealed envelope having an ionizable medium therein, a pair of spaced apart main groups of electrodes Within said envelope each group comprising a pair of spaced apart anodes and a thermionic cathode intermediate said anodes and electrically connected thereto, each of said main groups of electrodes defining one end of a bi-directional main current path through said device, and an auxiliary group of electrodes comprising an auxiliary anode and an auxiliary thermionic cathode surrounded by an apertured constricting electrode, said auxiliary group of electrodes being arranged on opposite sides of said main current path whereby an auxiliary discharge is substantially perpendicular through said main current Path.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,544,513 Stutsman Mar. 6, 1951 2,602,862 Webster July 8, 1952 

